d2948937a0 introduced code to read Heightmap images into RM terrain
data. However, the original diff contained a bug where it read
Out-of-bounds array data for grayscale images. This bug was hidden by
another issue until D1816 / cbc04ba83b, which changed the code and made
the OOB read actually relevant. The effect was twofold:
- The height chosen was not the max of the 3 color channels, but the max
of the 3 neighboring pixel (thus slightly lowering the quality of
generated maps)
- The height for the bottom-right coordinates were random memory values,
thus garbage.
This random height ended up resulting in non-deterministic map
generation, which was reported on Ngorongoro.
The cause of this silent failure is that the transformation to BGRA is
not applied for grayscale images, as the alpha transformation is
processed first and exits. This is not per-se buggy, so it is not
changed here.
The fixed behaviour is specialized for the common grayscale case, and
retains the max-of-3-color-channel intended behaviour otherwise.
Fixes#6261.
Reported by: Feldfeld
Differential Revision: https://code.wildfiregames.com/D4203
This was SVN commit r25843.
